This application discloses an improved limp home feature for an electronic throttle control. An electronic throttle control (ETC) replaces mechanical throttle linkage to control opening of the throttle valve. The throttle valve actuated by the ETC is opened proportionally according to signals received from a sensor placed on an accelerator pedal. The ETC opens the throttle valve proportionally to movement of the accelerator pedal.
A typical ETC will be mounted to a throttle body. The throttle body includes a bore to intake air. The throttle valve is disposed within the bore to regulate the intake of air. The throttle valve is attached to a shaft rotatably mounted to the throttle body. Rotation of the shaft opens the throttle valve. The shaft will extend from the throttle body to attach to the ETC. A precision stop for a closed throttle position is set to provide a minimum airflow requirement for an engine. The minimum airflow requirement will put an engine at or near a stall condition. The air passage can be opened to a greater extent by the valve to provide additional airflow as required for specific engine operating conditions.
In an ETC application a second throttle position is set when power is removed from the ETC. The second throttle position provides an engine speed that will produce enough power that can easily be controlled by a driver. This second position is referred to by those knowledgeable in the art as the limp home throttle valve position. The intent of the limp home position is to provide the driver with sufficient power to maneuver the vehicle.
The engine speed required for the limp home setting must be set precisely, because a limp home engine speed that is too low will not provide the necessary engine power to maneuver the vehicle. Alternatively, too high an engine speed may create a sensation in the driver of being out of control of the vehicle. For these reasons it is desirable and necessary to provide a mechanism that provides for the precise reliable setting of both the closed throttle valve position and the limp home throttle valve position for an ETC.
The subject invention is an electronic throttle control with a linkage assembly that provides for the precise setting of a closed throttle valve position and a limp home throttle valve position. Essentially, an arrangement allows a precise amount of throttle movement from a closed throttle position to the limp home throttle position when the ETC motor is disabled. The linkage assembly is preferably mounted to the side of a throttle body. The throttle body includes a bore having a first shaft that extends through the bore. A throttle valve is attached to the first shaft within the bore and rotates with the first shaft to regulate air intake. A lever is rigidly attached to the first shaft. The lever is driven by an electronic throttle control. A stop bracket provides for a precision first stop position of the lever in the throttle valve closing direction. The stop bracket includes first and second arms that define an opening. The opening includes a length between inner surfaces of the first and second arms. A stop is mounted to a pin and disposed within the opening of the stop bracket. A biasing member biases the stop bracket in an open throttle direction. The ETC overcomes the biasing member in the closed throttle direction to reach the first stop position. The first stop position corresponds to the closed throttle position. The stop is adjustable to allow for setting of the first stop position. The limp home engine speed is set by the second stop position of the stop bracket. The second stop position is a predetermined distance from the first stop position that remains the same regardless of the setting of the first stop position. The predetermined distance between the first stop position and the second stop position is a difference between a width of the opening and a width of the stop. The biasing member possess enough force to overcome all forces in the closing throttle position except for those forces exerted by the ETC. Upon loss of power to the ETC the biasing member will force the stop bracket to the second stop position, and thereby move the lever and throttle valve to a limp home position.
The subject invention overcomes the deficiencies of the prior art by providing a simple, precise, reliable and cost effective linkage assembly for setting both the closed throttle and the limp home throttle positions.